The invention relates to a tire comprising at least one tread joined to two beads by means of two sidewalls and a carcass reinforcement, said tire being able to be used with or without an independent inner tube and being intended, after mounting on a standardized rim and after inflation, to be fitted on any vehicle capable of rolling.
Application FR A 2 771 150, filed Nov. 14, 1997, describes a tire which is intended to be mounted on a rim of axial width L, with rim seats forming an angle xcex3 with the axis of rotation such that 0xc2x0xe2x89xa6xcex3xe2x89xa616xc2x0, and rim flanges with rounded hooks. Said tire comprises a tread joined to two beads by two sidewalls and at least one carcass reinforcement formed of at least one ply of reinforcement elements, each bead being devoid of a bead wire, and said carcass reinforcement having in each bead a meridian profile which is curved axially and radially from the outside to the inside to form an axially inner edge located in an angle xcex1 open axially and radially towards the inside, one of the sides of which is parallel to the axis of rotation, and of a value of at most 25xc2x0. Said carcass reinforcement is reinforced in each bead, at least radially to the outside and axially to the inside, by at least one first continuous additional layer of meridian profile substantially parallel to the meridian profile of said carcass reinforcement in the bead and comprising at least one first section composed of at least one ply formed of inextensible reinforcement elements forming an angle of between xe2x88x922.5xc2x0 and +2.5xc2x0 with the circumferential direction, the radially upper end of said additional ply being distant from the axis of rotation by an amount at least equal to 0.96 times the distance between said axis and that point of the corresponding flange of the mounting rim which is farthest from said axis of rotation, and the axially inner end being distant from the equatorial plane by an amount at most 0.43 times the width L of the mounting rim.
It is then possible better to control the distribution of the contact pressures between the rim and the tire at the level of the respective rim and bead seats while permitting an improvement in the resistance to unwinding of the carcass reinforcement in the event of a high degree of heating of the beads without using anchoring bead wires for the carcass reinforcement.
In the case of tires having a high recommended inflation pressure, the document cited mentions that the first additional layer may be formed of two sections of several additional plies of inextensible reinforcement elements, superposed on one another, the lengths of which may or may not be the same. The presence of another continuous additional reinforcement layer arranged radially to the inside and axially to the outside has proved very advantageous. Said layers are for the most part formed of inextensible cables, preferably metal ones, forming an angle of between xe2x88x922.5xc2x0 and +2.5xc2x0 with the circumferential direction.
Although such structures make it possible to solve the problems posed, they do not have sufficient endurance, owing to the appearance and propagation of breaks in the carcass reinforcement due to the variation of curvature of the meridian profile of said reinforcement during travel, which variation is between the curvature when the meridian in question passes into the contact ellipse and when it is opposite to said ellipse.
In order to overcome said problems of endurance, the tire according to the invention, which is intended to be mounted on a rim, the seats of which form an angle xcex3 with the axis of rotation such that 0xc2x0xe2x89xa6xcex3xe2x89xa616xc2x0, and the rim flanges of which have rounded hooks, comprising a tread joined to two beads devoid of bead wires by two sidewalls and at least one carcass reinforcement formed of at least one ply of reinforcement elements, and having in each bead a meridian profile which is curved axially and radially from the outside to the inside to form an axially inner edge located in an angle open axially and radially towards the inside, one of the sides of which is parallel to the axis of rotation, and of a value of at most 25xc2x0, said carcass reinforcement being reinforced in each bead at least radially to the outside and axially to the inside by at least one first continuous additional layer, composed of at least one ply formed of inextensible reinforcement elements forming an angle of between xe2x88x922.5xc2x0 and +2.5xc2x0 with the circumferential direction, is characterized in that said carcass reinforcement is also, radially to the outside and axially to the inside, reinforced by a second continuous additional layer, composed of at least one ply formed of inextensible radial reinforcement elements, the two additional layers having meridian profiles substantially parallel to the meridian profile of the carcass reinforcement in the bead and the radially upper ends of said first and second additional layers being distant from the axis of rotation by amounts at least equal respectively to 0.96 times and 1.20 times the distance between said axis and that point of the corresponding flange of the mounting rim which is farthest from said axis of rotation.
xe2x80x9cRim flange, viewed in meridian sectionxe2x80x9d is to be understood to mean the assembly formed by the section substantially perpendicular to the axis of rotation extended, firstly, radially to the outside, by a circular section, forming what is sometimes referred to as the rim hook, and secondly, radially to the inside, by the arc of a circle connecting the axially outer end of the rim seat to said assembly.
xe2x80x9cMeridian profile of a carcass reinforcement in a beadxe2x80x9d is to be understood to mean the meridian profile of the geometric center line of said reinforcement, viewed in meridian section, said profile being considered radially to the inside of a straight line parallel to the axis of rotation of the mounting rim and of the tire passing through the point of the rim hook, corresponding to the bead in question, farthest from the axis of rotation.
xe2x80x9cInextensible reinforcement elementxe2x80x9d is to be understood to mean a cable or a monofilament having a relative elongation of at most 1.5% under a force of 20% of the breaking load. The first and second additional layers will preferably be formed of metal cables or monofilaments, preferably of steel, in the case of tires of the xe2x80x9cheavy vehiclexe2x80x9d or xe2x80x9cconstructionxe2x80x9d type, but may advantageously be formed of textile elements, preferably of aromatic polyamide, in the case of tires for aeroplanes, agricultural tractors or passenger cars, for example.
The endurance of the tire will be improved further if the thickness of rubber existing between the center line of the meridian profile of the carcass reinforcement and the outer wall of the bead, over the length of contact between the bead and the rim, is reduced by the length of contact between the bead and rim seats respectively, which is at least equal to 0.02% of the maximum axial width of the carcass reinforcement.
A large number of rims and tires may be covered by the invention; the meridian profile of the assembly formed by the carcass reinforcement and the additional layers, which profile is very closely linked to the profile of the carcass reinforcement, will, within a bead, be advantageously adapted to the meridian profile of the rim on which said bead will be mounted. The meridian profile of the additional plies in effect does not differ from the meridian profile of the carcass reinforcement, except by the possible variation of the rubber decoupling layer(s), whether or not reinforced, existing between the two reinforcements, which explains why said profiles are said to be substantially parallel. The meridian profile of the second additional layer may be strictly parallel to the profile of the carcass reinforcement, with a single layer of rubber of constant thickness separating the two profiles. The meridian profile of the second layer may be substantially parallel to the profile of the carcass reinforcement, with one or more plies of the first additional layer possibly being inserted radially between the carcass reinforcement and the second additional layer, whereas the remaining ply (plies) of the first layer are radially to the outside and axially to the inside of the second additional layer.
Said meridian profile of the carcass reinforcement in a bead may be formed, passing radially and axially towards the inside, possibly by a first, concave, arc of a circle extended tangentially by a second, convex, arc of a circle, said second arc of a circle possibly being extended tangentially by a straight line segment.
The radially outer end of the first, concave, arc of a circle is firstly radially distant from the axis of rotation by an amount equal to the radius of the circle which is the geometric locus of the points of the rim flange which are farthest from said axis, and secondly axially distant from the equatorial plane by an amount which lies between two values, the rim width increased by 10% of said width and the rim width reduced by 10% of said width. Said radially outer end is also the point of tangency with the convex meridian profile of the carcass reinforcement in the sidewall. The center of curvature of the first arc of a circle, relative to the two axes which are the trace of the equatorial plane and the axis of rotation, has the same coordinates as the center of curvature of the rim hook. As for the length of said first arc of a circle of the carcass reinforcement profile, it is at the least zero, the meridian profile of the carcass reinforcement in the bead beginning directly with the second, convex, arc of a circle and at the most equal to the length of an arc of a circle the radially lower end of which would be the point of tangency of said arc with a line perpendicular to the axis of rotation.
Said first arc of a circle is tangentially extended radially and axially to the inside by a second arc of a circle of a radius of curvature which may be between a minimum value of 5 mm and a maximum value equal to the radius of curvature of the meridian profile of the carcass reinforcement in the sidewall measured at the point of tangency between said profile and the first arc of a circle, said maximum value being the value of radius used preferably when the first arc of a circle has a length of zero.
The second arc of a circle is possibly tangentially extended radially and axially to the inside by a straight line segment, the axially inner end of which is also the end of the meridian profile of the carcass reinforcement. The axially inner edge of the meridian profile is composed either of part of the second arc of a circle to which the straight line segment is added, or of part of an arc of a circle. Said edge is the part of the meridian profile located in an angle defined by a half line forming a tangent to the second arc of a circle and forming with the axis of rotation an angle of 25xc2x0 and a half line parallel to said axis of rotation, the origin of which is precisely the point of tangency of the second arc of a circle with the half line oriented at 25xc2x0.
The first additional layer has an axially inner end which may be closer to or farther away from the equatorial plane than the axially inner end of the carcass reinforcement. Between its axially inner end and the vertex of the angle in which the edge of the meridian profile of the carcass reinforcement is located, the first additional layer may be separated from the second additional layer by a small thickness of rubber mix, a total of the respective two thicknesses of the calendering layers of the two adjacent plies, whereas between said vertex and the radially upper end said thickness is between 1.0 and 1.8 times the thickness previously mentioned. As for the second additional layer, its axially inner end is distant axially from the equatorial plane by an amount substantially equal to the axial distance between the axially inner end and the carcass reinforcement in the bead. Between its radially upper and axially inner ends, said second additional layer is advantageously separated from the carcass reinforcement and/or the first additional layer by a thickness which is the total of the two thicknesses of the calendering layers of the adjacent layers.
In the case of a high inflation pressure, the presence of a third continuous additional reinforcement layer may also prove very advantageous. Said third layer, axially to the outside and radially to the inside of at least the radially innermost and axially outermost ply of the carcass reinforcement, also has a meridian profile substantially parallel to the meridian profile of said carcass reinforcement in the bead. Said layer is formed of at least one ply of reinforcement elements. It may be continuous and homogenous over its entire length from its radially upper end which may be located radially to the outside, but preferably radially to the inside, of the straight line parallel to the axis of rotation of the rim and passing through that point of the rim flange, corresponding to the bead in question, which is farthest from the axis of rotation, to its axially inner end closest to the equatorial plane. It is then advantageously formed of inextensible cables, preferably metal ones, forming an angle of between xe2x88x922.5xc2x0 and +2.5xc2x0 with the circumferential direction.
In the case in which its radially upper end is radially to the inside of the straight line parallel to the axis of rotation and passing through that point of the rim flange which is farthest from said axis of rotation, said third additional layer may also be nonhomogenous over its width, although continuous, and it is then advantageously formed of two sections: a first section included between its radially upper end and a point located between the center of the second arc of a circle of the meridian profile of the carcass reinforcement in the bead and the vertex of the angle in which the edge of the carcass reinforcement is located, and a second section, extending the first section axially to the inside and radially to the inside and included between said point and its radially lower end axially closest to the equatorial plane. The first section is formed of at least one ply of inextensible cables, preferably metal ones made of steel, forming an angle of between xe2x88x922.5xc2x0 and +2.5xc2x0 with the circumferential direction, while the second section is advantageously formed of at least one ply of reinforcement elements, said ply having the properties of being only very slightly compressible in the transverse direction and advantageously extensible in the circumferential direction, which, firstly, permits simple and reproducible control of the pressures exerted by the bead seat on the rim seat, the inventors having unexpectedly noted that said pressures were a function of the resistance to tension of the reinforcement elements constituting the ply (plies) of the second section of the second additional layer, and, secondly, facilitates the laying during manufacture of said additional layer.
Said second section may advantageously be formed of at least one ply:
either of continuous, circumferential reinforcement elements, preferably metal ones referred to as xe2x80x9celasticxe2x80x9d, that is to say, having a relative elongation of at least 1.5% under a tensile force equal to 20% of the breaking load;
or of undulating or zigzag reinforcement elements of circumferential average orientation, preferably metal ones;
or of rows of discontinuous, circumferential reinforcement elements, preferably metal ones, each element having a circumferential length which may be between 0.1 and 1 times the circumferential length of the ply and the spaces between elements being offset meridianly relative to the spaces of the axially adjacent rows and said elements or rows of elements, however in this case being parallel to each other and practically adjoining in the transverse direction;
or of metal reinforcement elements oriented at an angle of at least 80xc2x0 relative to the circumferential direction, said elements being circumferentially separated from each other by a distance of at least 0.2 mm.
Furthermore, the laying of the second section of the third layer may be facilitated further if the ply (plies) of said section are formed of strips of several circumferential reinforcement elements, which strips are circumferentially discontinuous, the discontinuity gaps between strips forming with the circumferential direction an angle which is different from the angle formed with the same direction by the reinforcement elements of the carcass reinforcement, the difference being at least 10xc2x0.
The position of the third layer and the plies which make it up may be a function of the number of plies forming the carcass reinforcement of the tire. If said carcass reinforcement is formed of at most three plies, the third additional layer is preferably located in its entirety axially to the outside and radially to the inside of the carcass ply which is radially farthest to the inside and axially farthest to the outside of the carcass reinforcement. On the other hand, if said carcass reinforcement is formed of at least four plies, the plies forming the third additional layer are preferably such that two of them tightly surround a group of carcass plies which may be formed of one or more carcass reinforcement plies.
The characteristics and advantages of the present invention will be better understood with reference to the following description which refers to the drawings.